CD-ROM

CD-ROM

Overview
A CD-ROM is a pre-pressed compact disc
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

 that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book”
Yellow Book (CD standard)
The Yellow Book is the standard that defines the format of CD-ROMs. The Yellow Book, created by Sony and Philips, was the first extension of the Red Book. It is named after one of a set of color-bound books that contain the technical specifications for all CD and CD-ROM formats.-External links:The...

 standard developed by Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

 and Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

 adapted the format to hold any form of binary data
Binary file
A binary file is a computer file which may contain any type of data, encoded in binary form for computer storage and processing purposes; for example, computer document files containing formatted text...

.

CD-ROMs are popularly used to distribute computer software, including video games and multimedia applications, though any data can be stored (up to the capacity limit of a disc).
Discussion
Ask a question about 'CD-ROM'
Start a new discussion about 'CD-ROM'
Answer questions from other users
Full Discussion Forum
 
Unanswered Questions
Recent Discussions
Encyclopedia
A CD-ROM is a pre-pressed compact disc
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

 that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book”
Yellow Book (CD standard)
The Yellow Book is the standard that defines the format of CD-ROMs. The Yellow Book, created by Sony and Philips, was the first extension of the Red Book. It is named after one of a set of color-bound books that contain the technical specifications for all CD and CD-ROM formats.-External links:The...

 standard developed by Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

 and Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

 adapted the format to hold any form of binary data
Binary file
A binary file is a computer file which may contain any type of data, encoded in binary form for computer storage and processing purposes; for example, computer document files containing formatted text...

.

CD-ROMs are popularly used to distribute computer software, including video games and multimedia applications, though any data can be stored (up to the capacity limit of a disc). Some CDs hold both computer data and audio with the latter capable of being played on a CD player
Compact disc player
A Compact Disc player , or CD player, is an electronic device that plays audio Compact Discs. CD players are often a part of home stereo systems, car audio systems, and personal computers. They are also manufactured as portable devices...

, while data (such as software or digital video) is only usable on a computer (such as ISO 9660
ISO 9660
ISO 9660, also referred to as CDFS by some hardware and software providers, is a file system standard published by the International Organization for Standardization for optical disc media....

 format PC CD-ROMs). These are called enhanced CD
Enhanced CD
Enhanced CD, also known as CD Extra and CD Plus, is a certification mark of the Recording Industry Association of America for various technologies that combine audio and computer data for use in both Compact Disc and CD-ROM players....

s.

Although many people use lowercase letters in this acronym, proper presentation is in all capital letters with a hyphen between CD and ROM. At the time of the technology's introduction it had more capacity than computer hard drives common at the time. The reverse is now true, with hard drives far exceeding CDs, DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

s and Blu-ray, though some experimental descendants of it such as HVDs
Holographic Versatile Disc
The Holographic Versatile Disc is an optical disc technology developed between April 2004 and mid-2008 that can store up to several terabytes of data on an optical disc the same size as a CD, DVD or Blu-ray disc. It employs a technique known as collinear holography, whereby a green and red laser...

 may have more space and faster data rates than today's biggest hard drive.

Media



CD-ROM discs are identical in appearance to audio CDs
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

, and data are stored and retrieved in a very similar manner (only differing from audio CDs in the standards used to store the data). Discs are made from a 1.2 mm thick disc of polycarbonate
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...

 plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

, with a thin layer of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 to make a reflective surface. The most common size of CD-ROM disc is 120 mm in diameter, though the smaller Mini CD
Mini CD
Mini CDs, or “pocket CDs” are CDs with a smaller diameter and one third the capacity.-Formats:Amongst the various formats are the* Mini CD single, a small disc. The format is mainly used for audio CD singles in certain regions , much like the old vinyl single...

 standard with an 80 mm diameter, as well as numerous non-standard sizes and shapes (e.g., business card-sized media) are also available.
Data is stored on the disc as a series of microscopic indentations. A laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 is shone onto the reflective surface of the disc to read the pattern of pits and lands ("pits", with the gaps between them referred to as "lands"). Because the depth of the pits is approximately one-quarter to one-sixth of the wavelength of the laser light used to read the disc, the reflected beam
Light beam
A light beam or beam of light is a narrow projection of light energy radiating from a source into a beam. Sunlight is a natural example of a light beam when filtered through various mediums...

's phase
Phase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

 is shifted in relation to the incoming beam, causing destructive interference and reducing the reflected beam's intensity. This pattern of changing intensity of the reflected beam is converted into binary data.

Standard


Several formats are used for data stored on compact discs, known as the Rainbow Books
Rainbow Books
The Rainbow Books are a collection of standards defining the formats of Compact Discs.Red BookYellow BookThe Rainbow Books are a collection of standards defining the formats of Compact Discs.Red Book...

. These include the original Red Book
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

 standards for CD audio, White Book and Yellow Book CD-ROM
Yellow Book (CD standard)
The Yellow Book is the standard that defines the format of CD-ROMs. The Yellow Book, created by Sony and Philips, was the first extension of the Red Book. It is named after one of a set of color-bound books that contain the technical specifications for all CD and CD-ROM formats.-External links:The...

. The ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

 10149 / ECMA
Ecma International
Ecma International is an international, private non-profit standards organization for information and communication systems. It acquired its name in 1994, when the European Computer Manufacturers Association changed its name to reflect the organization's global reach and activities...

-130 standard, which gives a thorough description of the physics and physical layer of the CD-ROM, inclusive of cross-interleaved Reed-Solomon coding
Cross-Interleaved Reed-Solomon Coding
In the compact disc system, cross-interleaved Reed-Solomon code provides error detection and error correction. CIRC adds to every three data bytes one redundant parity byte.-Overview:...

 (CIRC) and eight-to-fourteen modulation
Eight-to-Fourteen Modulation
Eight-to-fourteen modulation is a data encoding technique – formally, a channel code – used by compact discs and pre-Hi-MD MiniDiscs. EFMPlus is a related code, used in DVDs and SACDs. EFM and EFMPlus were both invented by Kees A...

 (EFM), can be downloaded from ISO or ECMA.

ISO 9660
ISO 9660
ISO 9660, also referred to as CDFS by some hardware and software providers, is a file system standard published by the International Organization for Standardization for optical disc media....

 defines the standard file system of a CD-ROM, although it is due to be replaced by ISO 13490
ISO 13490
ISO/IEC 13490 is the successor to ISO 9660 , intended to describe the file system of a CD-ROM or CD-R....

 (which also supports CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....

 and multi-session). UDF
Universal Disk Format
Universal Disk Format is an implementation of the specification known as ISO/IEC 13346 and ECMA-167 and is an open vendor-neutral file system for computer data storage for a broad range of media. In practice, it has been most widely used for DVDs and newer optical disc formats, supplanting ISO 9660...

 extends ISO 13346 (which was designed for non-sequential write-once
Write Once Read Many
A Write Once Read Many or WORM drive is a data storage device where information, once written, cannot be modified. On ordinary data storage devices, the number of times data can be modified is not limited, except by the rated lifespan of the device, as modification involves physical changes that...

 and re-writeable discs such as CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....

 and CD-RW
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....

) to support read-only and re-writeable media and was first adopted for DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

. The bootable CD specification, to make a CD emulate a hard disk or floppy, is called El Torito
El Torito (CD-ROM standard)
The El Torito Bootable CD Specification is an extension to the ISO 9660 CD-ROM specification. It is designed to allow a computer to boot from a CD-ROM...

.

CD-ROM drives are rated with a speed factor relative to music CDs (1× or 1-speed which gives a data transfer rate of 150 KiB/s). 12× drives were common beginning in early 1997. Above 12× speed, there are problems with vibration and heat. Constant angular velocity (CAV) drives give speeds up to 30× at the outer edge of the disc with the same rotational speed as a standard constant linear velocity (CLV) 12×, or 32× with a slight increase. However due to the nature of CAV (linear speed at the inner edge is still only 12×, increasing smoothly in-between) the actual throughput increase is less than 30/12 – in fact, roughly 20× average for a completely full disc, and even less for a partially filled one.

Problems with vibration, owing to e.g. limits on achievable symmetry and strength in mass produced media, mean that CD-ROM drive speeds have not massively increased since the late 90s. Over 10 years later, commonly available drives vary between 24× (slimline and portable units, 10× spin speed) and 52× (typically CD- and read-only units, 21× spin speed), all using CAV to achieve their claimed "max" speeds, with 32× through 48× most common. Even so, these speeds can cause poor reading (drive error correction having become very sophisticated in response) and even shattering of poorly made or physically damaged media, with small cracks rapidly growing into catastrophic breakages when centripetally stressed at 10,000 – 13,000 rpm (i.e. 40–52× CAV). High rotational speeds also produce undesirable noise from disc vibration, rushing air and the spindle motor itself. Thankfully, most 21st century drives allow forced low speed modes (by use of small utility programs) for the sake of safety, accurate reading or silence, and will automatically fall back if a large number of sequential read errors and retries are encountered.

Other methods of improving read speed were trialled such as using multiple optical beams, increasing throughput up to 72× with a 10× spin speed, but along with other technologies like 90~99 minute recordable media and "double density" recorders, their utility was nullified by the introduction of consumer DVDROM drives capable of consistent 36× CD-ROM speeds (4× DVD) or higher. Additionally, with a 700 MB CD-ROM fully readable in under 2½ minutes at 52× CAV, increases in actual data transfer rate are decreasingly influential on overall effective drive speed when taken into consideration with other factors such as loading/unloading, media recognition, spin up/down and random seek times, making for much decreased returns on development investment. A similar stratification effect has since been seen in DVD development where maximum speed has stabilised at 16× CAV (with exceptional cases between 18× and 22×) and capacity at 4.3 and 8.5 GiB (single and dual layer), with higher speed and capacity needs instead being catered to by Blu-ray drives.

CD-ROM format


A CD-ROM sector contains 2,352 byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...

s, divided into 98 24-byte frames. Unlike a music CD, a CD-ROM cannot rely on error concealment by interpolation
Interpolation
In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points....

, and therefore requires a higher reliability of the retrieved data. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed–Solomon error correction
Reed–Solomon error correction
In coding theory, Reed–Solomon codes are non-binary cyclic error-correcting codes invented by Irving S. Reed and Gustave Solomon. They described a systematic way of building codes that could detect and correct multiple random symbol errors...

. A Mode-1 CD-ROM, which has the full three layers of error correction data, contains a net 2,048 bytes of the available 2,352 per sector. In a Mode-2 CD-ROM, which is mostly used for video files, there are 2,336 user-available bytes per sector. The net byte rate of a Mode-1 CD-ROM, based on comparison to CDDA audio standards, is 44100 Hz × 16 bits/sample × 2 channels × 2,048 / 2,352 /8 = 153.6 kB/s = 150 KiB/s. The playing time is 74 minutes, or 4,440 seconds, so that the net capacity of a Mode-1 CD-ROM is 682 MB or, equivalently, 650 MiB.

A 1× speed CD drive reads 75 consecutive sectors per second.

CD sector contents
  • A standard 74 min. CD contains 333,000 blocks or sector
    Disk sector
    In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. Each sector stores a fixed amount of user data. Traditional formatting of these storage media provides space for 512 bytes or 2048 bytes of user-accessible data per sector...

    s.
  • Each sector is 2,352 bytes, and contains 2,048 bytes of PC (mode 1) data, 2,336 bytes of PSX/VCD (mode 2) data, or 2,352 bytes of audio.
  • The difference between sector size and data content are the header information and the error-correcting code
    Error detection and correction
    In information theory and coding theory with applications in computer science and telecommunication, error detection and correction or error control are techniques that enable reliable delivery of digital data over unreliable communication channels...

    s, that are big for data (high precision required), small for VCD (standard for video) and none for audio. Note that all of these, including audio, still benefit from a lower layer of error correction at a sub-sector level.
  • If extracting the disc in raw format (standard for creating images) always extract 2,352 bytes per sector, not 2,048/2,336/2,352 bytes depending on data type (basically, extracting the whole sector). This fact has two main consequences:
    • Recording data CDs at very high speed (40×) can be done without losing information. However, as audio CDs do not contain a third layer of error-correcting code
      Error detection and correction
      In information theory and coding theory with applications in computer science and telecommunication, error detection and correction or error control are techniques that enable reliable delivery of digital data over unreliable communication channels...

      s, recording these at high speed may result in more unrecoverable errors or 'clicks' in the audio.
    • On a 74 minute CD, one can fit larger images using raw mode, up to 333,000 × 2,352 = 783,216,000 bytes (~747 MiB). This is the upper limit for raw images created on a 74 min or ~650 MiB Red Book
      Red Book (audio CD standard)
      Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

       CD. The 14.8% increase is due to the discarding of error correction data
    • The sync pattern for Mode 1 CDs is 0x00ffffffffffffffffffff00
  • An image size is always a multiple of 2,352 bytes (the size of a block) when extracting in raw mode.

Layout type ← 2,352 byte block →
CD digital audio: 2,352
Digital audio
CD-ROM (mode 1): 12
Sync.
4
Sector id.
2,048
Data
4
Error detection
8
Zero
276
Error correction
CD-ROM (mode 2): 12
Sync.
4
Sector id.
2,336
Data


Manufacture



Pre-pressed CD-ROMs are mass-produced by a process of stamping where a glass master disc is created and used to make "stampers", which are in turn used to manufacture multiple copies of the final disc with the pits already present. Recordable (CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....

) and rewritable (CD-RW
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....

) discs are manufactured by a different method, whereby the data are recorded on them by a laser changing the properties of a dye or phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

 material in a process that is often referred to as "burning
Optical disc authoring
Optical disc authoring, including DVD and Blu-ray Disc authoring , is the process of assembling source material—video, audio or other data—into the proper logical volume format to then be recorded onto an optical disc .-Process:To burn an optical disc, one usually first creates an...

".

Capacity



CD-ROM capacities are normally expressed with binary prefixes, subtracting the space used for error correction data. A standard 120 mm, 700 MB CD-ROM can actually hold about 737 MB (703 MiB) of data with error correction (or 847 MB total). In comparison, a single-layer DVD-ROM can hold 4.7 GB of error-protected data, more than 6 CD-ROMs.
Capacities of Compact Disc types (90 and 99 minute discs are not standard)
Type Sectors Data max. size Audio max. size Time
(MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...

)
Approx. (MiB
Mebibyte
The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220, therefore 1 mebibyte is . The unit symbol for the mebibyte is MiB. The unit was established by the International Electrotechnical Commission in 2000 and has been accepted for use by all major...

)
(MB) (min
Minute
A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...

)
8 cm 94,500 193.536 184.570 222.264 21
283,500 580.608 553.711 666.792 63
650 MB 333,000 681.984 650.391 783.216 74
700 MB 360,000 737.280 703.125 846.720 80
800 MB 405,000 829.440 791.016 952.560 90
900 MB 445,500 912.384 870.117 1,047.816 99
Note: megabyte (MB) and minute (min) values are exact; MiB values are approximate.

CD-ROM drives


CD-ROM discs are read using CD-ROM drives. A CD-ROM drive may be connected to the computer via an IDE (ATA), SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

, SATA
Serial ATA
Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives...

, FireWire
IEEE 1394 interface
The IEEE 1394 interface is a serial bus interface standard for high-speed communications and isochronous real-time data transfer, frequently used by personal computers, as well as in digital audio, digital video, automotive, and aeronautics applications. The interface is also known by the brand...

, or USB
Universal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....

 interface or a proprietary interface, such as the Panasonic CD interface
Panasonic CD interface
The Panasonic CD interface, also known as the MKE CD interface , SLCD or simply Panasonic, is a proprietary computer interface for connecting a CD-ROM drive to an IBM PC compatible computer...

. Virtually all modern CD-ROM drives can also play audio CDs
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

 as well as Video CD
Video CD
Before the advent of DVD and Blu-ray, the Video CD became the first format for distributing films on standard 120 mm optical discs. The format is a standard digital format for storing video on a Compact Disc...

s and other data standards when used in conjunction with the right software.

CD-ROM drive can sometimes be a misnomer for newer drives that are capable for reading and burning DVDs, the CD's successor which is now the standard optical disc drive.

Laser and optics


CD-ROM drives employ a near-infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 780 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...

 laser diode
Laser diode
The laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current...

. The laser beam is directed onto the disc via an opto-electronic tracking module, which then detects whether the beam has been reflected or scattered.

Transfer rates


If a CD-ROM is read at the same rotational speed as an audio CD, the data transfer rate is 150 KiB/s, commonly referred to as "1×". At this data rate, the track moves along under the laser spot at about 1.2 m/s. To maintain this linear velocity as the optical head moves to different positions, the angular velocity is varied from 500 rpm at the inner edge to 200 rpm at the outer edge.
By increasing the speed at which the disc is spun, data can be transferred at greater rates. For example, a CD-ROM drive that can read at 8× speed spins the disc at 1600 to 4000 rpm, giving a linear velocity of 9.6 m/s and a transfer rate of 1200 KiB/s. Above 12× speed most drives read at Constant angular velocity
Constant angular velocity
In optical storage, constant angular velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs...

 (CAV, constant rpm) so that the motor is not made to change from one speed to another as the head seeks from place to place on the disc. In CAV mode the "×" number denotes the transfer rate at the outer edge of the disc, where it is a maximum.
20× was thought to be the maximum speed due to mechanical constraints until Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...

 Electronics introduced the SCR-3230, a 32x CD-ROM drive which uses a ball bearing
Bearing (mechanical)
A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...

 system to balance the spinning disc in the drive to reduce vibration and noise. As of 2004, the fastest transfer rate commonly available is about 52× or 10,400 rpm and 7.62 MiB/s. Higher spin speeds are limited by the strength of the polycarbonate plastic of which the discs are made. At 52×, the linear velocity of the outermost part of the disk is around 65 m/s. However, improvements can still be obtained by the use of multiple laser pickups as demonstrated by the Kenwood
Kenwood Electronics
is a Japanese manufacturer of amateur radio as well as Hi-Fidelity and portable audio equipment.-History:The company first started in 1946 as the Kasuga Radio Co. Ltd. In Komagane City, Nagano Prefecture, Japan. In 1960 the firm was renamed "Trio Corporation"...

 TrueX 72× which uses seven laser beams and a rotation speed of approximately 10×.

CD-Recordable drives are often sold with three different speed ratings, one speed for write-once operations, one for re-write operations, and one for read-only operations. The speeds are typically listed in that order; i.e. a 12×/10×/32× CD drive can, CPU and media permitting, write to CD-R discs at 12× speed (1.76 MiB/s), write to CD-RW discs at 10× speed (1.46 MiB/s), and read from CDs at 32× speed (4.69 MiB/s).

The 1× speed rating for CD-ROM (150 KiB/s) is different than the 1× speed rating for DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

s (1.32 MiB/s).



Common data transfer speeds for CD-ROM drives
Transfer speed KiB/s Mbit/s RPM
150 1.23 200–500
300 2.46 400-1,000
600 4.92 800–2,000
1,200 9.83 1,600–4,000
10× 1,500 12.3 2,000–5,000
12× 1,800 14.7 2,400–6,000
20× 1,200–3,000 up to 24.6 4,000 (CAV)
32× 1,920–4,800 up to 39.3 4,800 (CAV)
36× 2,160–5,400 up to 44.2 7,200 (CAV)
40× 2,400–6,000 up to 49.2 8,000 (CAV)
48× 2,880–7,200 up to 59.0 9,600 (CAV)
52× 3,120–7,800 up to 63.9 10,400 (CAV)
56× 3,360–8,400 up to 68.8 11,200 (CAV)
72× 6,750–10,800 up to 88.5 2,000 (multi-beam)

Copyright issues


There has been a move by the recording industry to make audio CDs (CDDAs, Red Book
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

 CDs) unplayable on computer CD-ROM drives, to prevent the copying of music. This is done by intentionally introducing errors onto the disc that the embedded circuits on most stand-alone audio players can automatically compensate for, but which may confuse CD-ROM drives. Consumer rights advocates are as of October 2001 pushing to require warning labels on compact discs that do not conform to the official Compact Disc Digital Audio standard (often called the Red Book
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

) to inform consumers which discs do not permit full fair use
Fair use
Fair use is a limitation and exception to the exclusive right granted by copyright law to the author of a creative work. In United States copyright law, fair use is a doctrine that permits limited use of copyrighted material without acquiring permission from the rights holders...

 of their content.

In 2005, Sony BMG Music Entertainment
Sony BMG Music Entertainment
Sony BMG Music Entertainment was a recorded music company, which was a 50–50 joint venture between the Sony Corporation of America and Bertelsmann AG...

 was criticised when a copy protection mechanism known as Extended Copy Protection
Extended Copy Protection
Extended Copy Protection is a software package developed by the British company First 4 Internet, and sold as a copy protection or digital rights management scheme for Compact Discs...

 (XCP) used on some of their audio CDs automatically and surreptitiously installed copy-prevention software on computers (see 2005 Sony BMG CD copy protection scandal
2005 Sony BMG CD copy protection scandal
The Sony BMG CD copy protection rootkit scandal concerns the copy protection measures included by Sony BMG on Compact Discs in 2005. Sony BMG included the Extended Copy Protection and MediaMax CD-3 software on music CDs. XCP was put on 52 titles and MediaMax was put on 50 titles...

). Such discs are not legally allowed to be called CDs or Compact Discs because they break the Red Book standard governing CDs, and Amazon.com for example describes them as "copy protected discs" rather than "compact discs" or "CDs".

Software distributors, and in particular distributors of computer games, often make use of various copy protection schemes to prevent software running from any media besides the original CD-ROMs. This differs somewhat from audio CD protection in that it is usually implemented in both the media and the software itself. The CD-ROM itself may contain "weak" sectors to make copying the disc more difficult, and additional data that may be difficult or impossible to copy to a CD-R or disc image, but which the software checks for each time it is run to ensure an original disc and not an unauthorized copy is present in the computer's CD-ROM drive.

Manufacturers of CD writers (CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....

 or CD-RW
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....

) are encouraged by the music industry to ensure that every drive they produce has a unique identifier, which will be encoded by the drive on every disc that it records: the RID or Recorder Identification Code. This is a counterpart to the The Source IDentification Code (SID)—the Source Identification Code, an eight character code beginning with "IFPI
IFPI
The International Federation of the Phonographic Industry is the organisation that represents the interests of the recording industry worldwide. It is a not-for-profit members' organisation registered in Switzerland...

" that is usually stamped on discs produced by CD recording plants.

See also

  • Computer hardware
    Computer hardware
    Personal computer hardware are component devices which are typically installed into or peripheral to a computer case to create a personal computer upon which system software is installed including a firmware interface such as a BIOS and an operating system which supports application software that...

  • CD shattering
    CD shattering
    CD shattering, DVD shattering and optical disc shattering , a phenomenon also known as exploding CDs, occurs when a optical disc shatters inside a high speed optical disc drive with a loud cracking sound. Typically, the disc and the drive will be ruined...

  • CD/DVD authoring
  • DVD-Audio
    DVD-Audio
    DVD-Audio is a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and is not the same as video DVDs containing concert films or music videos....

  • DVD-ROM
    DVD
    A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

  • MultiLevel Recording
    MultiLevel Recording
    MultiLevel Recording was a technology originally developed by Optex Corporation and promoted by Calimetrics to increase the storage capacity of optical discs. It failed to establish itself on the market...

    , an obsolete technology (with non-binary modulation)
  • Optical disc drive
  • Phase-change Dual
    Phase-change Dual
    Phase-Change Dual is a rewritable optical disc format introduced by Panasonic in 1995. Much like CD-RW, PD uses a phase change layer that can be overwritten in a single pass of the read/write head. A PD disc has a capacity of 650 MB, can be rewritten 500,000 times and is enclosed in a protective...

  • Red Book (audio CD standard)
    Red Book (audio CD standard)
    Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

  • Thor-CD
    Thor-CD
    Thor-CD was a recordable CD format proposed in 1988 by Tandy , that was never released in commercial version.At the time Tandy proposed the new format, CDs were mostly used for digital music, but not for other digital data...